1. Technical Field
This invention relates to railway vehicles and steering trucks therefor. More particularly, this invention relates to railway locomotives and motorized self-steering radial trucks for locomotive use.
2. Background
Conventional railway truck designs comprising a pair of laterally spaced side frames, at least one transom and a plurality of axle and wheel sets extending transversely there between have become the standard in many railway industry applications. Problems encountered with these conventional trucks include the tendency for the wheel sets to traverse curves in a non-radial orientation and with much wheel flange to rail rubbing contact. Furthermore, the wheel sets may tend to slide during negotiation of track curves. Such rubbing contact and wheel sliding result in undesirable high wheel and rail wear, and the flange rubbing in particular may produce a tendency for the wheel to climb the rail. Improper wheel set tracking in curves may also result in track misalignment. Additionally, curved track imposes lateral forces on the wheel sets tending to displace them laterally off the truck center line, as shown in FIG. 1. These lateral forces cause increased wear of wheel set bearings and other truck components.
Other related problems occur when conventional trucks traverse straight, or tangent, runs of track. For example, a rigid wheel axle set, having conventional tapered conical wheels, when displaced laterally from the center line of a run of straight track, executes two simultaneous motions; first, the wheel set moves toward its equilibrium (center) position under the influence of gravity, and secondly, the high side wheel, rolling on a larger diameter than the low side wheel, moves along the rail faster than its partner, causing the wheel set to yaw. Given the proper set of circumstances, this motion may become a sustained harmonic oscillation known as hunting. The hunting tendency is transmitted to the truck and causes an oscillatory yawing motion of the truck about its center of rotation, resulting in additionally high truck component, wheel and rail wear.
These problems have been recognized in the prior art and a variety of self steering railway truck designs have been devised which purport to allow the wheel sets to track without sliding and without undue flange rubbing 25 during negotiation of curves, and with minimal adverse consequences resulting from hunting.
One example is Goding, U.S. Pat. No. 4,765,250, which teaches a method for inducing an "equal and opposite" rotation, or yaw, of one truck axle in response to the yawing of another truck axle when the truck is encountering a curve. Four traction rods, rotatably connected to the two axles near each wheel, and connected at their other ends to two transversely mounted steering arms transmit the tractive force to a lower end of respective vertical shafts. Attached to the top of each of the vertical shafts are opposing crank arms which themselves are interconnected by a diagonal alignment arm. As one axle yaws, that yawing motion is transmitted via the traction rods, steering arm, vertical shaft, crank arm and diagonal alignment arm to induce a purported "equal and opposite" yawing motion in the other axle.
Equal and opposite yawing of the two axles is required for the two wheel sets to accurately follow a curved track of constant radius, as shown in FIG. 2. It can be demonstrated trigonometrically, however, as shown in FIGS. 3 and 4, that the rigid diagonal connecting link of Goding cannot induce an "equal and opposite" rotation of the axles.
Referring to FIGS. 3 and 4, the free body diagram of FIG. 3 depicts the Goding two axle, diagonal connecting link steerable truck of the present invention in parallel axle, straight track operation. It is a four pin, one link system, wherein tractive force is transmitted from the wheels to the truck frame through pins P.sub.1 and P.sub.2 about which axles 28 and 29 approximately pivot. Pins P.sub.3 and P.sub.4 are used to transmit axle rotating forces through diagonal link 37. First and second axles 28, 29 respectively, are separated by a longitudinal distance L and are pivotally connected by diagonal link 37 having length l.sub.s. FIG. 4 shows the steerable truck of FIG. 3 during curved track operation wherein an angulation of degree .theta..sub.1 has been induced in first axle 28. Diagonal link 37 has length l.sub.c. Through displacement of link 37, an opposite angulation of degree .theta..sub.2 is induced in axle 29. The trigonometric proof that equal and opposite angulation of axle 29 cannot occur, is as follows:
Referring to FIGS. 3 and 4:
R=distance from center of axle to a wheel PA1 L=distance between axles PA1 l.sub.s =length of diagonal arm during straight track operation PA1 l.sub.c =length of diagonal arm during curved track operation PA1 .theta..sub.1 =yaw angle of front axle during curved track operation PA1 .theta..sub.2 =yaw angle of rear axle during curved track operation EQU 1.sub.s.sup.2 =L.sup.2 +(2R) EQU l.sub.s =[L.sup.2 +4R.sub.2 ] 1/2
Referring now specifically to FIG. 4 (induced angulation) with origin (0,0) at the center of axle 28 ##EQU1## EQU For all 0&lt;.theta.&lt;90.degree.:4R.sup.2 cos.sup.2 .theta.&lt;4R.sup.2
Therefore l.sub.c &lt;l.sub. s for equal and opposite angulation of the two axles. It is necessarily true, then, that for l.sub.c =l.sub.s (a rigid diagonal connecting link), equal and opposite angulation cannot occur. It is only by accidental, or incidental, tolerance "slop", that the Godinq design works. Adding a second rigid diagonal connecting link at the opposite set of opposing axle ends will bind the system.
Considerable other prior work has been done in the area of self steering railway trucks, but no design enjoys the advantageous features of the present invention. Designs which have employed a direct mechanical diagonal linking of the ends of two axles are inherently incapable of producing equal and opposite axle alignment, and would bind up in operation were there not enough slop in the system to allow the axles to give.
Accordingly, it is an object of this invention to provide a self-steering railway truck in which a true "equal and opposite" rotation of the end axles occurs, so that a curved railway truck track path is accurately followed, thereby minimizing wheel and rail wear.
Another object of the present invention is to provide a self-steering railway truck in which hunting, with its concomitant adverse affects, is minimized, by minimizing axle and wheel set yawing and lateral displacement during straight track operation.
It is a further object of the present invention to provide a self-steering railway truck in which the angulated end axles have an inherent tendency to return to straight track operation when straight track is encountered after self-steering operation on a curved section of track.
Yet another object of the present invention is to provide a self-steering railway truck which automatically self- adjusts, or compensates, for wheel, self-steering apparatus, or other truck component wear.